1. Field of the Application
The present application relates to an axial turbomachine fitted with a compressor. More specifically the present application relates to a compression stage for an axial turbomachine compressor. More specifically the present application relates to the sealing of a compression stage for an axial turbomachine compressor.
2. Description of Related Art
An axial turbomachine compressor usually has several compression stages, each of which is formed by the combination of a rotor blade row and a stator blade row. In order to channel the flow axially in the compression stage, the latter has coaxial shells. In particular, each stator blade row is provided with an internal shell which is fixed to the inner tips of the stator blades. Such an inner shell has an annular shape and surrounds the rotor. Some functional play where they join is part of the design.
In operation, leakage can occur between the rotor and the inner shell because of this play. This leakage tends to reduce the effective compression of each compression stage and reduces the pressure at the compressor outlet. To enhance the output pressure axial turbomachines compressors are fitted with seals. These devices can be fitted at each compression stage, at the interface between the inner shell and the rotor.
They may include an annular layer of abradable material which is advantageously fitted on the stator in order to reduce the rotating mass. This is intended to mate abrasively with lip seals or annular slats which are formed on the outer surface of the rotor. To save material, the layer of abradable material can be divided into two annular layers. They are arranged upstream and downstream of the inner shell. The latter may have the shape of an inverted “U”, the inner ends of the branches of which support layers of abradable material. This “U” shape is a recess which saves weight.
U.S. Pat. No. 7,695,244 B2 discloses a bladed compressor with an inner shell. The latter is formed with a central platform and two radial extensions terminating in return walls. The return walls each have annular bands of abradable material that are intended to come into contact with the lip seals formed on a radial rotor. The platform, the extensions and the return walls define a cavity that is large in comparison with that defined between the lip seals. This cavity configuration forms a reservoir to stem a localized and short leak. However, it is not possible to significantly improve the seal between the inner shell and the rotor during steady state operation.
Although great strides have been made in the area of axial compressors, many shortcomings remain.